Repairing a amplifier need assistance .

#12

Joined Nov 30, 2010
18,224
Don't know what I did but now it reads 5 ohms not 0.00
Fumble fingers!:p

Do you mean you have the nice and proper 5 ohms now that you put the resistors back in?
And what DC voltage can you measure across them? We're trying to be sure the idle current is right before soldering in the power transistors.
 

Thread Starter

Mr.oaktree

Joined Dec 10, 2014
68
Ok ok ..... maybe I'm just teeny weeny fumble fingered lol :p
R18 = .042 R17 = .006 and yes 5 ohms nice and proper when both soldered in
 

#12

Joined Nov 30, 2010
18,224
R-11 and R-12 Both at 56v
Therefore, not a problem. You measured across those 2 resistors and got equal voltages. If you read carefully, I said to measure AT those resistors. That means "to ground". That would have gotten you the 15 volts I claimed would be there. Amiright?
 

#12

Joined Nov 30, 2010
18,224
Ok ok ..... maybe I'm just teeny weeny fumble fingered lol :p
R18 = .042 R17 = .006 and yes 5 ohms nice and proper when both soldered in

R17 has to carry the current coming through R13
R18 has to carry the current coming through R14

One of your measurements is 7 times as high as the other. Your R17 measurement is not even close to 0.38 as previously measured. They should be balanced.

Go to post 38 and do what I said there.
 

#12

Joined Nov 30, 2010
18,224
R11 = 17.5v+ R12 = 16.5v-
That's the voltages on zeners d3 and d8. So they're off a bit. I don't think it matters today. Those are error sensing circuits. Hoping they shut down any important parts while the speaker melted. :rolleyes:

You really must pay more attention to positive and negative voltages. Not declaring + or - could cause us problems pretty soon.
 

#12

Joined Nov 30, 2010
18,224
Pin 7 reads 0.o75v+ .
ok ill start stating neg or pos
Looks good. The op-amp is happy... or burned up :eek:
That doesn't matter right now. It is not biasing the driver circuit anywhere except zero volts and that is good for right now.
If you can prove the idle current in the R13, Q1, R17, R18, Q2, to R14 path is equal and opposite, you are ready to solder in power transistors.
You haven't done that yet.

I am tired.
We've been on this for 4 hours.
Time for a break, and I think that means both of us.
We've been fighting measurement errors most of the time today.
 

Thread Starter

Mr.oaktree

Joined Dec 10, 2014
68
If it helps ..... I took measurements on other channel . Ch1 . R1-17 =.213v+
R1-18 = .137v-
This channel actually works and produces sound .. but voltages do not match either .....
 

#12

Joined Nov 30, 2010
18,224
So why aren't our voltages matching ??
I'm calling fumble fingers.:(
Your measurements have been all over the place today.
The currents HAVE to match if the schematic properly represents the circuit.
The machine worked last week, so it must have been right last week.
Either you prove the currents match or find out where some of it escaped.
Best suspects are Q1 and Q2
If one of them went bad, we have to find out which one and replace it. (or just shotgun both of them)
If you can't get the current flows to match pretty closely, we have a bad driver.
If you can't measure the same voltage across a resistor (within 500%) twice, something is still badly wrong.

I suggest you and I take a break before we start calling each other names.
Oops. Too late. I already did that.:oops:
 
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